Yay, finally our Trigonometry final is almost here. I'm taking the test this tuesday, and have been reviewing today. One thing I've had a lot of trouble with is finding the correct sign on problems where I have to rewrite a trigonometric identity in terms of another. For example: Write tanx in terms of sinx, x is in Quadrant 4. tanx = -sinx/cosx (-sinx because sinx is negative in Q4) tanx = -sqrt(-sinx/sqrt(1-sin2x) I am assuming sinx is negative because it is in Quadrant 4. Yet the answer in the book says the fraction is positive. Yet... Write tanx in terms of cosx; x in Quadrant 2: this should have negative cosine values so tanx = -sqrt(1-cos2x)/cosx is a correct answer in the back of the book. Can anyone clarify anything about rewriting these with the correct sign values?